An update must have been made to my Mastodon instance. Now even when I select the "Mobile" layout in the preferences, instead of showing a single column like before, it shows 3 columns again, one for posting, one with my timeline, and one with navigation links. I tried selecting various other options, but the only difference between them is whether 3 or 4 columns are displayed.
The only way I found to get it to display a single column again is to resize the browser less wide.
https://wedistribute.org/2019/04/your-guide-to-alternative-frontends-for-mastodon-and-pleroma/
https://pinafore.social/ - this is an alternative web front-end with a single column display and multiple color options.
Pinafore user guide: https://github.com/nolanlawson/pinafore/blob/master/docs/User-Guide.md
The only way I found to get it to display a single column again is to resize the browser less wide.
https://wedistribute.org/2019/04/your-guide-to-alternative-frontends-for-mastodon-and-pleroma/
https://pinafore.social/ - this is an alternative web front-end with a single column display and multiple color options.
Pinafore user guide: https://github.com/nolanlawson/pinafore/blob/master/docs/User-Guide.md